Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2×1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

Semicontinuous Bioreactor Production of Recombinant Butyrylcholinesterase in Transgenic Rice Cell Suspension Cultures.

An active and tetrameric form of recombinant butyrylcholinesterase (BChE), a large and complex human enzyme, was produced via semicontinuous operation in a transgenic rice cell suspension culture. After transformation of rice callus and screening of transformants, the cultures were scaled up from culture flask to a lab scale bioreactor. The bioreactor was operated through two phases each of growth and expression. The cells were able to produce BChE during both expression phases, with a maximum yield of 1.6 mg BChE/L of culture during the second expression phase. Cells successfully regrew during a 5-day growth phase. A combination of activity assays and Western blot analysis indicated production of an active and fully assembled tetramer of BChE.

An aerosol climatology for a rapidly growing arid region (southern Arizona): Major aerosol species and remotely sensed aerosol properties.

This study reports a comprehensive characterization of atmospheric aerosol particle properties in relation to meteorological and back trajectory data in the southern Arizona region, which includes two of the fastest growing metropolitan areas in the United States (Phoenix and Tucson). Multiple data sets (MODIS, AERONET, OMI/TOMS, MISR, GOCART, ground-based aerosol measurements) are used to examine monthly trends in aerosol composition, aerosol optical depth (AOD), and aerosol size. Fine soil, sulfate, and organics dominate PM2.5 mass in the region. Dust strongly influences the region between March and July owing to the dry and hot meteorological conditions and back trajectory patterns. Because monsoon precipitation begins typically in July, dust levels decrease, while AOD, sulfate, and organic aerosol reach their maximum levels because of summertime photochemistry and monsoon moisture. Evidence points to biogenic volatile organic compounds being a significant source of secondary organic aerosol in this region. Biomass burning also is shown to be a major contributor to the carbonaceous aerosol budget in the region, leading to enhanced organic and elemental carbon levels aloft at a sky-island site north of Tucson (Mt. Lemmon). Phoenix exhibits different monthly trends for aerosol components in comparison with the other sites owing to the strong influence of fossil carbon and anthropogenic dust. Trend analyses between 1988 and 2009 indicate that the strongest statistically significant trends are reductions in sulfate, elemental carbon, and organic carbon, and increases in fine soil during the spring (March-May) at select sites. These results can be explained by population growth, land-use changes, and improved source controls.

Implantation of a black diaphragm intraocular lens for traumatic aniridia.

PURPOSE: To evaluate the suitability and safety of a black diaphragm posterior chamber intraocular lens (IOL). SETTING: Department of Ophthalmology, Leeds General Infirmary, Leeds, United Kingdom. METHODS: Seven patients who had secondary implantation of a Morcher 67G black diaphragm posterior chamber IOL were identified. All patients were men with a mean age of 42 years who had previous ocular trauma resulting in extensive loss of iris tissue (traumatic aniridia). Simultaneous penetrating keratoplasty was performed in 4 cases. Minimum follow-up was 10 months (mean 19 months). RESULTS: Best corrected visual acuity improved in 5 cases and was unchanged in 1 case. The lens was well centered in 5 cases. Two cases developed secondary glaucoma, 1 requiring trabeculectomy. One case developed infective endophthalmitis but had a visual acuity of 6/18 at last follow-up, and 1 had a vitreous and anterior chamber hemorrhage, which resolved. CONCLUSIONS: The black diaphragm posterior chamber IOL overcame aphakia in eyes with considerable loss of iris tissue and may mitigate the visually disabling effects of traumatic aniridia. Although this lens appears safe, caution should be used in its implantation until more patients with longer follow-up are studied.

Natural history of central topographic islands following excimer laser photorefractive keratectomy.

PURPOSE: To assess the incidence and natural history of central corneal topographic islands following excimer laser photorefractive keratectomy (PRK) and photoastigmatic refractive keratectomy (PARK). SETTING: A dedicated corneal diseases and refractive surgery unit within a National Health Service Trust ophthalmology unit in the United Kingdom. METHODS: Corneal topographic analysis was performed in a prospective study of 100 eyes of 75 consecutive patients who had PRK. All PRK/PARK excimer laser photorefractive procedures were performed by two surgeons observing a standardized protocol using a VISX 20/20 excimer laser. Mean preoperative myopic error was 5.54 diopters (D) +/- 3.44 (SD). Corneal topographic analysis was performed on all eyes preoperatively, 1 week postoperatively, and monthly thereafter for a minimum of 6 months or until central islands, if present, resolved. All patients had a minimum 12 months follow-up. RESULTS: Postoperatively, 29 eyes (29%) demonstrated central corneal topographic islands of greater than 3.00 D topographic power by computerized videokeratography (CVK). All central islands were identified in the first 4 weeks postoperatively. In all cases the differential dioptric power, created by the central islands within the ablation zone, decreased rapidly; within 6 months, 26 (90%) central islands had fully resolved without further treatment, and the remaining 3 (10%) resolved within 1 year of photorefractive surgery. The occurrence of central islands was related to higher preoperative myopic spherical equivalent (P = .01), greater attempted laser correction (P = .01), and greater projected depth of ablation (P = .01) (Student's two-tailed t-test). CONCLUSIONS: Central corneal topographic islands occurred in a significantly higher proportion of eyes having excimer laser photorefractive surgery than previously believed. The islands were associated with decreased unaided vision, reduced best spectacle-corrected acuity, and other troublesome visual symptoms; however, the central islands, along with their associated visual effects, usually resolved without surgical intervention within 6 months postoperatively.

Psychological aspects of excimer laser surgery for myopia: reasons for seeking treatment and patient satisfaction.

AIMS: To determine the reasons patients seek excimer laser treatment for myopia and to measure levels of patient satisfaction with each phase of this relatively new treatment. METHODS: A unique 38 item visual analogue questionnaire was developed and applied to 100 consecutive patients (n = 100) who had undergone excimer laser photorefractive keratectomy for myopia or myopic astigmatism at a single centre. All subjects underwent extensive ophthalmic assessment and patient education before treatment. RESULTS: A 90% response rate was achieved (n = 90). Improved unaided vision (85.6%), freedom from spectacles (83.3%), and difficulties with contact lens wear (72.7%) were the most common reasons for seeking treatment. The majority of patients felt that the quality of their life had improved (85.5%) and 82% felt that the quality of their unaided vision was as good as they had anticipated. overall, 95.5% of patients were pleased that they had undergone this procedure. The vast majority (98.9%) of patients felt that they fully understood the operation pretreatment but almost one quarter (23.9%) found the actual operation distressing. Only 15.7% found postoperative pain did not respond adequately to prescribed analgesia. CONCLUSIONS: This study demonstrates a very high level of patient satisfaction after excimer laser treatment for myopia and myopic astigmatism. It suggests that most patients seek treatment to enjoy better vision free from optical aids and that a high level of patient education preoperatively may establish realistic expectations and satisfaction with overall outcome.

Decentration of photorefractive keratectomy ablation zones after excimer laser surgery for myopia.

PURPOSE: To devise a method for measuring excimer laser photorefractive keratectomy (PRK) ablation zone decentration. SETTING: Excimer Laser Clinic, Sunderland Eye Infirmary, Sunderland Tyne and Wear, England. METHODS: Fifty-three eyes of 53 consecutive patients having PRK for a spherical myopic refractive error were studied. Preoperative and postoperative corneal topographic maps and differential subtraction maps were produced for each cornea. Using these maps, the distance between ablation zone centers and pupil centers was measured. All measurements were repeated by a second observer. RESULTS: Mean ablation zone decentration was 0.46 mm from the pupil center; 69% of cases decentered 0.50 mm or less. The difference between the two independent measurements was 0.05 +/- 0.06 mm (mean +/- SD). A trend toward superonasal displacement was noted. CONCLUSION: This simple method of measuring zone decentration can be used to compare the refractive results of PRK with those of other procedures.

Corneal topographic lagoons: a potential new marker for post-traumatic recurrent corneal erosion syndrome.

BACKGROUND: Post-traumatic recurrent corneal erosion syndrome is a common clinical problem in which a definitive diagnosis is not always possible based solely upon biomicroscopic corneal signs. Indeed, in some cases archetypical symptoms or a preceding history of epithelial trauma cannot always be elucidated. METHODS: Four groups of patients underwent corneal analysis using computer videokeratography. Group 1 (n = 11), subjects who presented with simple corneal epithelial trauma approximately three months before the study. Group 2 (n = 11), prospective analysis of subjects presenting with simple corneal epithelial trauma. Group 3 (n = 12), prospective analysis subjects with an established diagnosis of post-traumatic recurrent erosion syndrome. Group 4 (n = 135), prospective analysis of healthy control subjects. RESULTS: Small, well delineated areas (1.0 to 1.5 mm in diameter) of markedly reduced corneal dioptric power (greater than 2 dioptres), which we have termed 'corneal topographic lagoons', were identified more commonly in eyes with recurrent corneal erosion syndrome and in eyes that had recently sustained corneal epithelial trauma; being found in 18.2% of Group 1, 9.1% of Group 2, 58.3% of Group 3 but only 1.5% of Group 4 (control). CONCLUSIONS: The identification of areas of focal abnormality in the corneas of patients with post-traumatic recurrent corneal erosion syndrome remains a significant clinical problem. Corneal topographic analysis has demonstrated a focal abnormality, the 'corneal topographic lagoon', which is much more prevalent in cases of recent corneal trauma and recurrent corneal erosion syndrome than in the 'normal' population. Computerised videokeratography therefore adds a new tool to the armamentarium of the clinician seeking to identify and locate abnormalities in these difficult cases.

Deep corneal stromal opacities associated with long term contact lens wear.

BACKGROUND: One male and three female long term contact lens wearers (mean age 30.3 years; range 26-33) demonstrated unusual deep corneal stromal opacities which were predominantly just anterior to Descemet's membrane. None had any history of corneal dystrophy. These opacities were more common centrally, but were also identified in the corneal periphery. METHODS: All patients underwent routine ophthalmic examinations and, where appropriate, slit-lamp photography and specular microscopy. RESULTS: Mean lens wear in years and hours per day was 14.3 (range 10-17) and 14.3 (range 12-16) respectively. Specular microscopy disclosed cell densities within normal limits (mean 3041.5 cells per mm2) and coefficient of variation of mean cell area; COV = 0.31. Refractive errors ranged from -12.25 D to +6.25 best vision sphere and all four subjects attained at least 6/9 Snellen visual acuity. The subjects' contact lens wearing history included low water content hydroxymethylmethacrylate (HEMA) contact lenses and high water content HEMA contact lenses. Stromal opacity density was observed to diminish over a period of months on cessation of contact lens wear in two cases. CONCLUSION: The possible causes of these rarely reported opacities are discussed.